The present invention relates to a process for the recovery of iodine employed in chemical processes. More particularly, it relates to iodine recovery for re-use in processes wherein iodine and/or iodine-containing compounds are employed, notably dehydrogenation processes.
Processes wherein certain hydrocarbons are converted to less saturated hydrocarbons by dehydrogenation in which iodine is employed are well known in the art. These dehydrogenation reactions include, for example, the conversion of paraffins to olefins and diolefins, of olefins to diolefins, of certain parrafins to aromatics (dehydrocyclization) and of alkyl aromatics to vinyl aromatics including dehydrocoupling as in the conversion of toluene to stilbene. Such iodinative dehydrogenation processes employ iodine as such or iodine in conjunction with oxygen whereby the hydrogen iodide simultaneously formed in the reactions is converted under the reaction conditions to elemental iodine. In some processes, there is also a concomitant production of organic and inorganic iodides as by-products. In order for such processes to be economically feasible, iodine utilization must be maintained at a high level which requires efficient recovery of the iodine from process streams containing it for re-use in the process. Also, the removal of iodine from reaction effluents has a salutary effect in some instances. In the production of stilbene, for example, by dehydrocoupling of toluene in the presence of iodine, the removal of inorganic iodine from the reaction effluent facilitates purification of the stilbene by distillation to a product having &gt; 99% purity which is essentially free of iodine. It is, accordingly, an object of the present invention to provide a process which provides for recovery of iodine from process streams at a high level of efficiency. Other objects and advantages of the invention will become apparent from the following description thereof.